1. Field of Invention
The present invention relates to a semiconductor device and a method of producing the same, more particularly relates to a semiconductor device applied to for example a source-follower circuit and a method of producing the same.
2. Description of the Related Art
In recent years, as a solid-state imaging device mounted on a camera-function mobile phone, a personal digital assistant (PDA), or other mobile device, for example from the viewpoint of the power consumption, a MOS type image sensor requiring a lower power voltage in comparison with a CCD image sensor is frequently used.
Japanese Patent Publication (A) No. 2002-51263 for example discloses the above MOS type image sensor, wherein, in for example a pixel circuit, a source-follower circuit is frequently used. In related art, in a source-follower circuit as disclosed in for example Japanese Patent Publication (A) No. 6-125422, a surface channel type MOS transistor is used. Note that, in recent surface channel type MOS transistors, an LDD region (extension region) having a lower concentration than a source/drain region is formed inside the source/drain region.
In recent surface channel type MOS transistors, in order to suppress the short channel effect, impurities having a conductivity type inverse to that of the source/drain region are implanted into the vicinity of a bottom portion of the gate electrode based on the constant electric field scaling rule. This implantation of impurities is called “Hallo implantation” or “pocket implantation”. Hereinafter, a region subjected to Hallo implantation or pocket implantation will be referred to as a “pocket region”.
On the other hand, in a source-follower circuit, the nearer the linearity characteristic of an output voltage to an input voltage, the broader the operation range and the broader the dynamic range that can be obtained.